Since the advent of a resist for KrF excimer laser (248 nm), an image forming method called chemical amplification is used as an image forming method for a resist so as to compensate for sensitivity reduction caused by light absorption. For example, the image forming method by positive chemical amplification is an image forming method of decomposing an acid generator in the exposed area upon exposure with excimer laser, electron beam, extreme-ultraviolet light or the like to produce an acid, converting an alkali-insoluble group into an alkali-soluble group by using the generated acid as a reaction catalyst in the baking after exposure (PEB: Post Exposure Bake), and removing the exposed area with an alkali developer.
As for the alkali developer used in the method above, various alkali developers have been proposed, and an aqueous alkali developer of 2.38 mass % TMAH (an aqueous tetramethylammonium hydroxide solution) is being used for general purposes.
Also, due to miniaturization of a semiconductor device, the trend is moving into a shorter wavelength of the exposure light source and a higher numerical aperture (higher NA) of the projection lens, and an exposure machine using an ArF excimer laser with a wavelength of 193 nm as a light source has been developed at present. Furthermore, for example, a so-called immersion method of filling a high refractive-index liquid (hereinafter sometimes referred to as an “immersion liquid”) between the projection lens and the sample, and an EUV lithography of performing the exposure to ultraviolet light at a shorter wavelength (13.5 nm) have been heretofore proposed as a technique for raising the resolution.
However, it is actually very difficult to find out an appropriate combination of a resist composition, a developer, a rinsing solution and the like necessary for forming a pattern with overall good performance, and more improvements are being demanded. In particular, the resolved line width of the resist becomes finer, and this requires to improve the line edge roughness performance of a line pattern and improve the in-plane uniformity of a pattern dimension.
Under these circumstances, various configurations have been recently proposed as the positive resist composition (see, for example, JP-A-2008-203639 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2007-114613, JP-A-2006-131739, and JP-A-2000-122295). On the other hand, as well as a positive resist composition predominating at present, a negative chemical amplification resist composition for pattern formation by alkali development is also being studied (see, for example, JP-A-2006-317803, JP-A-2006-259582, JP-A-2006-195050, and JP-A-2000-206694). Because, in the production of a semiconductor device or the like, patterns having various profiles such as line, trench and hole need to be formed and some patterns are difficult to form by the current positive resist.
In recent years, a pattern forming method using a negative developer, that is, an organic solvent-containing developer, is also being developed (see, for example, JP-A-2008-281974, JP-A-2008-281975, and JP-A-2008-292975).
In the pattern formation by alkali development using the conventional negative resist, it is demanded to more improve the line width variation (LWR), focus latitude (DOF) and other various performances, which are presumed to be ascribable mainly to swelling at the development.
A double developing technique as a double patterning technology for further raising the resolution is described in JP-A-2008-292975, where by making use of such a property that when exposed, the polarity of a resin in a resist composition becomes high in the high light intensity region and is maintained as low in the low light intensity region, the high exposure region of a specific resist film is dissolved with a high-polarity developer and the low exposure region is dissolved with an organic solvent-containing developer, whereby the region of medium exposure dose is allowed to remain without being dissolved at the development and a line-and-space pattern having a pitch half the pitch of the exposure mask is formed.